Description
The 3500/70M-01-00 is a specialized module for the Bently Nevada 3500 series machinery protection system. Unlike standard vibration monitors, the 70M (Reciprocating Impulse) is specifically engineered to monitor the unique mechanical behaviors of reciprocating compressors.
It focuses on detecting “impulse” events—sharp, high-frequency spikes—that indicate loose parts, broken valves, or liquid slugging within a compressor cylinder.
Availability and Procurement
- Condition: New Original (Factory Sealed) or Refurbished (Standardized Industrial Bench Testing)
- Warranty: 12-month technical replacement warranty.
- Lead Time: Typically ships within 3–5 business days.
- Pricing: Subject to market supply for legacy 3500 modules; contact our sales team for a formal quote.
Model Code Breakdown (3500/70M-01-00)
- 3500/70M: Reciprocating Impulse Monitor (4-channel).
- -01: I/O Module Type: Discrete I/O with Internal Terminations.
- -00: Agency Approval: None / Standard (for non-hazardous or general industrial locations).
Technical Specifications
The 70M module processes signals from accelerometers or velocity transducers to calculate “Impulse” and “Acceleration” variables.
| Parameter | Specification |
| Channels | 4 channels per module |
| Input Sensors | Accelerometers (standard) or Pressure Transducers |
| Data Extraction | Peak Acceleration, Impulse Velocity, and Cylinder Pressure |
| Relay Drive | Drives internal or external 3500/32 or 3500/33 relay modules |
| Power Consumption | 7.0 Watts (Typical) |
| Isolation | 500 V DC between signal and rack ground |
| Configuration | Software-defined via 3500 Rack Configuration Software |
Core Functionality: Reciprocating Compressor Protection
Standard vibration monitoring (Proximity probes) is often ineffective for reciprocating machines because their motion is inherently “clunky” and non-sinusoidal. The 3500/70M uses specialized algorithms to solve this:
1. Impulse Detection (Loose Parts)
The monitor looks for high-frequency impacts that occur within a specific window of the crank cycle. This is critical for identifying loose piston nuts, broken valve plates, or liquid carryover before they result in a catastrophic cylinder head failure.
2. Crank-Angle Triggering
By using a Keyphasor (3500/25) signal, the 70M can “time” its monitoring. It knows when valves should open and close based on the position of the crankshaft. If it detects an impulse at the wrong time in the cycle, it can trigger an alarm or a trip.
3. Trending for Predictive Maintenance
The module provides “Direct” and “Peak” values to the 3500/92 Communication Gateway. This allows engineers to trend the degradation of valves over months, moving from reactive “fix-on-fail” maintenance to a predictive strategy.
Engineering Insights: Deployment and Maintenance
1. Sensor Selection and Mounting
The 70M typically relies on piezoelectric accelerometers mounted directly on the cylinder head or valve covers.
- Critical Constraint: The mounting must be metal-to-metal and extremely rigid. Use a threaded stud with a light film of oil. If the sensor is loose, the “Impulse” readings will be erratic, leading to nuisance alarms.
2. I/O Configuration (Internal Terminations)
The -01 option means the field wiring connects directly to the back of the 3500 rack.
- Best Practice: Ensure the cable shields are grounded at the 3500 rack only. If you ground the shields at both the sensor and the rack, you will create a ground loop that can introduce “noise” into the impulse calculation, which the 70M may mistake for a mechanical impact.
3. Threshold Tuning (The “Nuisance” Trip Risk)
Because reciprocating compressors are naturally loud and violent, setting the “Danger” trip level is a delicate balance.
- Strategy: During commissioning, record the baseline impulse levels at different load steps (0%, 25%, 50%, 100%). Set your alarm levels based on these baseline “signatures” plus a safety margin, rather than using generic factory defaults.
4. Hardware/Software Compatibility
Warning: The 3500/70M requires a specific minimum firmware version for the 3500/22M Transient Data Interface (TDI). If you are adding this module to an older 3500 rack, you may need to flash the TDI firmware to ensure the rack recognizes the new 70M module.
FAQ
Q: Can I use this for crosshead monitoring?
A: Yes, the 70M is commonly used for crosshead vibration and impact monitoring to detect loose crosshead pins or clearance issues.
Q: What is the difference between the 70M and the 72M?
A: The 70M is for Reciprocating Impulse (mechanical impacts), whereas the 72M is specifically for Reciprocating Rod Position (monitoring the wear of rider bands).
Q: Can this module be “Hot-Swapped”?
A: Yes, the 3500/70M is designed to be hot-swapped while the rack is powered. However, if the module is tied to an active “Trip” logic, ensure the associated relay channels are bypassed before pulling the module to prevent a spurious machine shutdown.
| BENTLY 3500/20 125744-02 |
| Bently Nevada 3500/15 133292-01 |
| Bently Nevada 3500/15 127610-01 |
